“Filling the tree” is a procedure used by the Senate Majority Leader to offer a sufficient number of amendments on legislation to “fill the tree” so that no other senator can offer an amendment.
Congressional Institute: “By tradition, the Majority Leader is recognized first at the start of a debate. This enables the Leader, from time to time, to block the minority from offering any changes to a bill. To accomplish this, the Majority Leader fills the amendment tree with extraneous or meaningless amendments thereby blocking the introduction of any legitimate amendments by any other Senator (including those in his own party). It is a form of parliamentary obstruction used by the majority.”